Question

591. Tag Validator

中文文档

Description

Given a string representing a code snippet, implement a tag validator to parse the code and return whether it is valid.

A code snippet is valid if all the following rules hold:

1. The code must be wrapped in a valid closed tag. Otherwise, the code is invalid.
2. A closed tag (not necessarily valid) has exactly the following format : <TAG_NAME>TAG_CONTENT</TAG_NAME>. Among them, <TAG_NAME> is the start tag, and </TAG_NAME> is the end tag. The TAG_NAME in start and end tags should be the same. A closed tag is valid if and only if the TAG_NAME and TAG_CONTENT are valid.
3. A valid TAG_NAME only contain upper-case letters, and has length in range [1,9]. Otherwise, the TAG_NAME is invalid.
4. A valid TAG_CONTENT may contain other valid closed tags, cdata and any characters (see note1) EXCEPT unmatched <, unmatched start and end tag, and unmatched or closed tags with invalid TAG_NAME. Otherwise, the TAG_CONTENT is invalid.
5. A start tag is unmatched if no end tag exists with the same TAG_NAME, and vice versa. However, you also need to consider the issue of unbalanced when tags are nested.
6. A < is unmatched if you cannot find a subsequent >. And when you find a < or </, all the subsequent characters until the next > should be parsed as TAG_NAME (not necessarily valid).
7. The cdata has the following format : <![CDATA[CDATA_CONTENT]]>. The range of CDATA_CONTENT is defined as the characters between <![CDATA[ and the first subsequent ]]>.
8. CDATA_CONTENT may contain any characters. The function of cdata is to forbid the validator to parse CDATA_CONTENT, so even it has some characters that can be parsed as tag (no matter valid or invalid), you should treat it as regular characters.

 

Example 1:

Input: code = "<DIV>This is the first line <![CDATA[<div>]]></DIV>"
Output: true
Explanation: 
The code is wrapped in a closed tag : <DIV> and </DIV>. 
The TAG_NAME is valid, the TAG_CONTENT consists of some characters and cdata. 
Although CDATA_CONTENT has an unmatched start tag with invalid TAG_NAME, it should be considered as plain text, not parsed as a tag.
So TAG_CONTENT is valid, and then the code is valid. Thus return true.

Example 2:

Input: code = "<DIV>>>  ![cdata[]] <![CDATA[<div>]>]]>]]>>]</DIV>"
Output: true
Explanation:
We first separate the code into : start_tag|tag_content|end_tag.
start_tag -> "<DIV>"
end_tag -> "</DIV>"
tag_content could also be separated into : text1|cdata|text2.
text1 -> ">>  ![cdata[]] "
cdata -> "<![CDATA[<div>]>]]>", where the CDATA_CONTENT is "<div>]>"
text2 -> "]]>>]"
The reason why start_tag is NOT "<DIV>>>" is because of the rule 6.
The reason why cdata is NOT "<![CDATA[<div>]>]]>]]>" is because of the rule 7.

Example 3:

Input: code = "<A>  <B> </A>   </B>"
Output: false
Explanation: Unbalanced. If "<A>" is closed, then "<B>" must be unmatched, and vice versa.

 

Constraints:

• 1 <= code.length <= 500
• code consists of English letters, digits, '<', '>', '/', '!', '[', ']', '.', and ' '.

Solutions

Solution 1

class Solution:
  def isValid(self, code: str) -> bool:
    def check(tag):
      return 1 <= len(tag) <= 9 and all(c.isupper() for c in tag)

    stk = []
    i, n = 0, len(code)
    while i < n:
      if i and not stk:
        return False
      if code[i : i + 9] == '<![CDATA[':
        i = code.find(']]>', i + 9)
        if i < 0:
          return False
        i += 2
      elif code[i : i + 2] == '</':
        j = i + 2
        i = code.find('>', j)
        if i < 0:
          return False
        t = code[j:i]
        if not check(t) or not stk or stk.pop() != t:
          return False
      elif code[i] == '<':
        j = i + 1
        i = code.find('>', j)
        if i < 0:
          return False
        t = code[j:i]
        if not check(t):
          return False
        stk.append(t)
      i += 1
    return not stk

class Solution {
  public boolean isValid(String code) {
    Deque<String> stk = new ArrayDeque<>();
    for (int i = 0; i < code.length(); ++i) {
      if (i > 0 && stk.isEmpty()) {
        return false;
      }
      if (code.startsWith("<![CDATA[", i)) {
        i = code.indexOf("]]>", i + 9);
        if (i < 0) {
          return false;
        }
        i += 2;
      } else if (code.startsWith("</", i)) {
        int j = i + 2;
        i = code.indexOf(">", j);
        if (i < 0) {
          return false;
        }
        String t = code.substring(j, i);
        if (!check(t) || stk.isEmpty() || !stk.pop().equals(t)) {
          return false;
        }
      } else if (code.startsWith("<", i)) {
        int j = i + 1;
        i = code.indexOf(">", j);
        if (i < 0) {
          return false;
        }
        String t = code.substring(j, i);
        if (!check(t)) {
          return false;
        }
        stk.push(t);
      }
    }
    return stk.isEmpty();
  }

  private boolean check(String tag) {
    int n = tag.length();
    if (n < 1 || n > 9) {
      return false;
    }
    for (char c : tag.toCharArray()) {
      if (!Character.isUpperCase(c)) {
        return false;
      }
    }
    return true;
  }
}

class Solution {
public:
  bool isValid(string code) {
    stack<string> stk;
    for (int i = 0; i < code.size(); ++i) {
      if (i && stk.empty()) return false;
      if (code.substr(i, 9) == "<![CDATA[") {
        i = code.find("]]>", i + 9);
        if (i < 0) return false;
        i += 2;
      } else if (code.substr(i, 2) == "</") {
        int j = i + 2;
        i = code.find('>', j);
        if (i < 0) return false;
        string t = code.substr(j, i - j);
        if (!check(t) || stk.empty() || stk.top() != t) return false;
        stk.pop();
      } else if (code.substr(i, 1) == "<") {
        int j = i + 1;
        i = code.find('>', j);
        if (i < 0) return false;
        string t = code.substr(j, i - j);
        if (!check(t)) return false;
        stk.push(t);
      }
    }
    return stk.empty();
  }

  bool check(string tag) {
    int n = tag.size();
    if (n < 1 || n > 9) return false;
    for (char& c : tag)
      if (!isupper(c))
        return false;
    return true;
  }
};

func isValid(code string) bool {
  var stk []string
  for i := 0; i < len(code); i++ {
    if i > 0 && len(stk) == 0 {
      return false
    }
    if strings.HasPrefix(code[i:], "<![CDATA[") {
      n := strings.Index(code[i+9:], "]]>")
      if n == -1 {
        return false
      }
      i += n + 11
    } else if strings.HasPrefix(code[i:], "</") {
      if len(stk) == 0 {
        return false
      }
      j := i + 2
      n := strings.IndexByte(code[j:], '>')
      if n == -1 {
        return false
      }
      t := code[j : j+n]
      last := stk[len(stk)-1]
      stk = stk[:len(stk)-1]
      if !check(t) || last != t {
        return false
      }
      i += n + 2
    } else if strings.HasPrefix(code[i:], "<") {
      j := i + 1
      n := strings.IndexByte(code[j:], '>')
      if n == -1 {
        return false
      }
      t := code[j : j+n]
      if !check(t) {
        return false
      }
      stk = append(stk, t)
      i += n + 1
    }
  }
  return len(stk) == 0
}

func check(tag string) bool {
  n := len(tag)
  if n < 1 || n > 9 {
    return false
  }
  for _, c := range tag {
    if c < 'A' || c > 'Z' {
      return false
    }
  }
  return true
}

impl Solution {
  pub fn is_valid(code: String) -> bool {
    fn check(tag: &str) -> bool {
      let n = tag.len();
      n >= 1 &&
        n <= 9 &&
        tag
          .as_bytes()
          .iter()
          .all(|b| b.is_ascii_uppercase())
    }

    let mut stk = Vec::new();
    let mut i = 0;
    while i < code.len() {
      if i > 0 && stk.is_empty() {
        return false;
      }
      if code[i..].starts_with("<![CDATA[") {
        match code[i + 9..].find("]]>") {
          Some(n) => {
            i += n + 11;
          }
          None => {
            return false;
          }
        };
      } else if code[i..].starts_with("</") {
        let j = i + 2;
        match code[j..].find('>') {
          Some(n) => {
            let t = &code[j..j + n];
            if !check(t) || stk.is_empty() || stk.pop().unwrap() != t {
              return false;
            }
            i += n + 2;
          }
          None => {
            return false;
          }
        };
      } else if code[i..].starts_with("<") {
        let j = i + 1;
        match code[j..].find('>') {
          Some(n) => {
            let t = &code[j..j + n];
            if !check(t) {
              return false;
            }
            stk.push(t);
          }
          None => {
            return false;
          }
        };
      }
      i += 1;
    }
    stk.is_empty()
  }
}